[linux-block.git] / tools / memory-model / litmus-tests / MP+polocks.litmus

C MP+polocks

(*
 * Result: Never
 *
 * This litmus test demonstrates how lock acquisitions and releases can
 * stand in for smp_load_acquire() and smp_store_release(), respectively.
 * In other words, when holding a given lock (or indeed after releasing a
 * given lock), a CPU is not only guaranteed to see the accesses that other
 * CPUs made while previously holding that lock, it is also guaranteed
 * to see all prior accesses by those other CPUs.
 *)

{}

P0(int *buf, int *flag, spinlock_t *mylock) // Producer
{
	WRITE_ONCE(*buf, 1);
	spin_lock(mylock);
	WRITE_ONCE(*flag, 1);
	spin_unlock(mylock);
}

P1(int *buf, int *flag, spinlock_t *mylock) // Consumer
{
	int r0;
	int r1;

	spin_lock(mylock);
	r0 = READ_ONCE(*flag);
	spin_unlock(mylock);
	r1 = READ_ONCE(*buf);
}

exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *)
Commit	Line	Data
1c27b644 PM	1	C MP+polocks
1c27b644 PM	2
8f32543b PM	3	(*
	4	* Result: Never
	5	*
	6	* This litmus test demonstrates how lock acquisitions and releases can
	7	* stand in for smp_load_acquire() and smp_store_release(), respectively.
	8	* In other words, when holding a given lock (or indeed after releasing a
	9	* given lock), a CPU is not only guaranteed to see the accesses that other
	10	* CPUs made while previously holding that lock, it is also guaranteed
	11	* to see all prior accesses by those other CPUs.
	12	*)
	13
5c587f9b	14	{}
1c27b644	15
b6ff3084	16	P0(int buf, int flag, spinlock_t *mylock) // Producer
1c27b644	17	{
acc4bdc5	18	WRITE_ONCE(*buf, 1);
1c27b644	19	spin_lock(mylock);
acc4bdc5	20	WRITE_ONCE(*flag, 1);
1c27b644 PM	21	spin_unlock(mylock);
	22	}
	23
b6ff3084	24	P1(int buf, int flag, spinlock_t *mylock) // Consumer
1c27b644 PM	25	{
	26	int r0;
	27	int r1;
	28
	29	spin_lock(mylock);
acc4bdc5	30	r0 = READ_ONCE(*flag);
1c27b644	31	spin_unlock(mylock);
acc4bdc5	32	r1 = READ_ONCE(*buf);
1c27b644 PM	33	}
1c27b644 PM	34
b6ff3084	35	exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *)